The present invention relates to an image processing apparatus used in a multi-functional apparatus, which can simultaneously carry out plural jobs, such as a scanning function to read manuscripts, a copying function to copy manuscripts and a printing function to make hard copies based on print data.
In order to reduce waiting time and to cater to the convenience of users, multiple jobs can be carried out simultaneously as long as the input/output devices are not used at the same time, in an image processing apparatus of a digital multifunctional apparatus featuring a scanning function, a copying function, a printing function and facsimile function. For example, while carrying out a printing operation of a manuscript requiring copying of plural paper sheets, carrying out a copy job, which will be used for the next printing cycle or while performing a scanning job, the sequential page printing job is carried out.
Generally, in order to carry out multiple-jobs simultaneously, image data from an input apparatus such as a scanner, etc. are arranged to be stored in an image memory device after being compressed, then the compressed data are read-out from the image memory device and output after extension is applied, when the essential output apparatus is available.
It is possible to carry out multiple input jobs or multiple output jobs simultaneously when plural input or plural output apparatuses are provided. However, it becomes impossible to carry out input jobs or output jobs simultaneously or efficiently due to the shortage of input or output devices when the number of the compression device or the extension (decompression) device falls short (for example, there is only one compression or extension device for each apparatus).
For example, it is possible to carry out a reading operation to scan a manuscript by a scanner and a receiving operation for print data simultaneously since the input devices used differ from each other. However, data processing speed is reduced when only one compression device is provided, since in order to carry out two-input processes simultaneously, the compression process for the scanning data and the compression process for a raster image, which has been converted from the printing data, on the same compression device, these processes have to be performed sequentially on the same compression device in a sequential page mode.
In order to overcome these problems, an image processing apparatus having plural compression devices to carry out compression process of image data read out by a scanner, and compression of a raster image converted from the print data, on two separate compression devices, has been proposed (for example, refer to a patent reference No. 1 listed below).
(Patent reference No. 1): Japanese Patent Application open for Public Inspection No. 2003-23543
In order to carry out an input process from a scanner etc., an output process to a printer etc., compression and extension processes of image data and a process to convert print data to a raster image, a buffer memory device is used to store the image data temporarily.
For example, print data is received simultaneously while copying, the following operations are carried out and access to the buffer memory device frequently occurs.    (1) An operation, which writes compressed image data captured by a scanner to the buffer memory device    (2) A reading operation of image data of (1) from the buffer memory device for image printing    (3) A writing operation of the image data, which has been converted to a raster image to the buffer memory device    (4) A reading operation of the image data of (3) for image compression    (5) A writing operation of the image data after a compression process has been applied    (6) A read out operation of the compressed data of (5) from the buffer memory device for storage on a hard disk apparatus. Then the accesses to the buffer memory are frequently conducted.
In a past it has been difficult to efficiently carry out plural jobs simultaneously even though plural compression devices are provided, since frequent access to the buffer memory device became a bottle neck.